Virtual path restoration scheme using fast dynamic mesh restoration in an optical network

ABSTRACT

A method for restoring a virtual path, provisioned between a source and a target node, in a mesh zoned optical network is described. The method, in one embodiment, broadcasts or floods restore path requests in the network to expedite the identification of an alternate route and minimize the service disruption for failed virtual path. The flooding of requests is controlled to ensure efficient performance of the network yet guaranteeing minimum restoration time to allow critical telecommunication related traffic to flow through the network with virtually no interruption. The constant update of nodal topology by each node allows a fast identification of alternate physical path for failed virtual path.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation of U.S. patentapplication Ser. No. 09/750,668, filed on Dec. 29, 2000, entitled“VIRTUAL PATH RESTORATION SCHEME USING FAST DYNAMIC MESH RESTORATION INAN OPTICAL NETWORK” (which is a Continuation-in-Part of patentapplication Ser. No. 09/232,397, filed Jan. 15, 1999, now U.S. Pat. No.6,856,627, entitled “A METHOD FOR ROUTING INFORMATION OVER A NETWORK,”having A. N. Saleh, H. M. Zadikian, Z. Baghdasarian, and V. Parsi asinventors), which is incorporated by reference herein in its entiretyand for all purposes. This application is assigned to Cisco Technology,Inc., the assignee of the present invention, and is hereby incorporatedby reference, in its entirety and for all purposes.

This application is also related to following applications:

-   -   1. Patent application Ser. No. 09/232,397, entitled “A NETWORK        ADDRESSING SCHEME FOR REDUCING PROTOCOL OVERHEAD IN AN OPTICAL        NETWORK”, filed Jun. 4, 1999 and having S. N. Ali and S. E.        Plote as inventors.    -   2. Patent application Ser. No. 09/232,395, entitled “A        CONFIGURABLE NETWORK ROUTER,”, filed Jan. 15, 1999 and        having H. M. Zadikian, A. N. Saleh, J. C. Adler, Z.        Baghdasarian, and V. Parsi as inventors.

Above mentioned applications are assigned to Cisco Technology, Inc., theassignee of the present invention, and are hereby incorporated byreference, in its entirety and for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of information networks, and moreparticularly relates to a protocol for configuring and restoring routesover a network.

2. Description of the Related Art

Today's networks carry vast amounts of information. High bandwidthapplications supported by these networks include streaming video,streaming audio, and large aggregations of voice traffic. In the future,these bandwidth demands are certain to increase. To meet such demands,an increasingly popular alternative is the use of lightwavecommunications carried over fiber-optic cables. The use of lightwavecommunications provides several benefits, including high bandwidth, easeof installation, and capacity for future growth.

Optical infrastructures are capable of transmission speeds in thegigabit range, which helps address the ever-increasing need forbandwidth mentioned above. Such infrastructures employ varioustopologies, including ring and mesh topologies. In order to providefault protection, ring topologies normally reserve a large portion (e.g.50% or more) of the network's available bandwidth for use in restoringfailed circuits. However, ring topologies are capable of quicklyrestoring failed circuits. This capability is important in providingreliable service to customers, and is particularly important intelephony applications, where a failure can result in alarms, droppedcalls, and, ultimately, customer dissatisfaction and lost revenue. In asimilar vein, because of bandwidth demands, protocol overhead related toprovisioning, restoration, and other functions should be kept to aminimum in order to make the maximum amount of bandwidth available foruse by customers.

An alternative to the ring topology, the mesh topology reduces theamount of bandwidth needed for protection. The mesh topology is apoint-to-point topology, with each node in the network connected to oneor more other nodes. Because a circuit may be routed through variouscombinations of the network's nodes and over the various links whichconnect them, excess capacity through a given node or over a given linkcan serve to protect several circuits. However, the restoration of acircuit following a failure in a mesh topology can consume a relativelylarge amount of time.

SUMMARY

In one embodiment, the present invention reduces the time and resourcesrequired to restore a failed virtual path in a mesh optical network bybroadcasting or ‘constrained flooding’ of restore path request packetsin the network. This carefully controlled ‘flooding’ of restore pathrequest packets quickly identifies multiple alternate paths for failedvirtual path thus allowing network to guarantee fast restoration timerequired for many telecommunication related connections.

In another embodiment, in case of a link port failure, the restorationis localized to the node where link port failure occurred. If a linkport failure occurs between two adjacent nodes then localization iseffected through restoration by the two adjacent nodes without theresource utilization of any other node or the network

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not intended to be in any way limiting. Otheraspects, inventive features, and advantages of the present invention, asdefined solely by the claims, will become apparent in the non-limitingdetailed description set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and numerous objects,features, and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 is a block diagram of a zoned network consisting of four zonesand a backbone.

FIG. 2 is a flow diagram of broad general steps performed by a node forrestoration in response to the failure of a virtual path.

FIG. 3A is a flow diagram of steps performed in response to failure of aport on a link between two adjacent neighbor nodes.

FIG. 3B illustrates an example of a Restore Span packet.

FIG. 3C illustrates an example of a Restore Span Response packet.

FIG. 3D illustrates an example of a Restore_I packet.

FIG. 4A is a flow diagram of general steps performed by a source orproxy node in response to the failure of a link.

FIG. 4B illustrates an example of a Restore Path Request (RPR) packet.

FIG. 5 illustrates the actions performed by tandem nodes in processingreceived RPR tests.

FIG. 6 illustrates the process performed at the target node once the RPRfinally reaches that node.

FIG. 7 Is a flow diagrams illustrating the processes performed byoriginating nodes that receive negative RPR responses.

FIG. 8 Is a flow diagrams illustrating the processes performed byoriginating nodes that receive negative RPR responses.

FIG. 9 is a block diagram illustrating network environment in acommercial transaction processing system.

FIG. 10 is a block diagram of a host computer system suitable forimplementing the present invention.

FIG. 11 illustrates the interconnection of host computer system toclient systems.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION OF THE INVENTION

The following is intended to provide a detailed description of anexample of the invention and should not be taken to be limiting of theinvention itself. Rather, any number of variations may fall within thescope of the invention which is defined in the claims following thedescription.

Network Architecture

To limit the size of the topology database used by some protocols, andto limit the scope of broadcast packets (e.g., packets used forrestoration), the nodes of a network can be divided into logical groups,referred to herein as “zones.” The use of zones provides severalbenefits. Networks employing zones can be implemented in severaldifferent ways, some of which can be implemented concurrently.

FIG. 1 illustrates an exemplary network that has been organized into abackbone, zone 100, and four configured zones, zones 101-104, which arenumbered 0-4 under the protocol, respectively. The exemplary networkemploys a type 0 node ID, as there are relatively few zones (4). Thesolid circles in each zone represent network nodes, while the numberswithin the circles represent node addresses, and include network nodes111-117, 121-126, 131-136, and 141-147. The dashed circles representnetwork zones. The network depicted in FIG. 1 has four configured zones(zones 101-104 (addressed as zones 1-4) and one backbone (zone 100(addressed as zone 0)). Nodes with node IDs 1.3, 1.7, 2.2, 2.4, 3.4,3.5, 4.1, and 4.2 (network nodes 113, 117, 122, 124, 134, 135, 141, and142, respectively) are boundary nodes because they connect to more thanone zone. All other nodes are interior nodes because their links attachonly to nodes within the same zone. Zone 100 consists of 4 nodes, zones101-104, with node IDs of 0.1, 0.2, 0.3, and 0.4, respectively.

Another example of the use of zone boundaries is in the provisioning andrestoration of circuits within the network. Zone boundaries can be usedto limit the flow of information generated by certain nodes during suchprovisioning and restoration. For example, a node can act as a proxynode for the source or destination node. In the event of a failure inthe network affecting the circuit between the two nodes, the proxy nodecan perform source or destination node related functions. In the case ofa failure, a node at the boundary of the zone, in which the failure hasoccurred, acts as a proxy for the source (or destination) node in theother zone. This avoids the need to involve the portion of the networkcircuit lying outside of the zone experiencing a failure, which would beexpected to remain unchanged.

Another example of localized restoration is the use of the nodes wherethe physical port failure between two adjacent nodes has occurred. Upondiscovering port failure, the two adjacent nodes restore the virtualpath without the involvement of any other node or the network as long asthere are sufficient ports available to restore failed link.

Initialization of Network Nodes

Once a network topology has been defined, the user can configure one ormore end-to-end communication connections that can span multiple nodesand zones, an operation that is referred to herein as provisioning. Eachset of physical connections that are provisioned creates an end-to-endcommunication connection between the two end nodes that supports avirtual point-to-point link (referred to herein as a virtual path orVP). Each link comprises a plurality of physical port between twoadjacent nodes. The resulting VP has an associated capacity and anoperational state, among other attributes.

VPs are also assigned a class of service, which determines theirrelative priority for restoration within the network. This class ofservice (CoS) is used during failure recovery procedures to determinewhich VPs are to be restored first and what restoration scheme isassociated with it.

With each VP is associated the notion of a Physical Instance. The firsttime that a VP is set up, the VP is assigned a Physical Instance of 1.Whenever a fully set up path for a VP has to be changed because of somefailure, the Physical Instance is incremented by 1. The source node ofVP maintains a field referred to as Physical Instance Identifier. Thisfield is preferably included in restoration related and otherconfiguration packets. Only the source node should be provided theability to update this parameter of a VP. The first path of any VP thatis successfully provisioned (as seen by the Source node) will typicallyhave a Physical Instance identifier of 1. All future Path relatedmessages (Restore_I, Restore_Path and like) will preferably have thecorrect value of this identifier. If a new path is selected for this VP,the source node of the VP, which originates Restore Path Requestpackets, will increment this identifier by 1. As will be discussedsubsequently, several Physical Instances of the same VP may temporarilyexist in the network at any given time due to the distributed nature ofpath selection (and multiple failures) during dynamic restoration.Embodiments of the present invention ensures that only one instancesurvives.

Failure Detection, Propagation, and Restoration

Failure Detection and Propagation

In networks, failures are typically detected using the mechanismsprovided by the underlying physical network. For example, when using aSONET network, a fiber cut on a given link results in a loss of signal(LOS) condition at the nodes connected by that link. The LOS conditionpropagates an Alarm Indication Signal (AIS) and Remote Defect Indication(RDI), and generates a LOS defect locally. The defect is upgraded to afailure 2.5 seconds later, which causes an alarm to be sent to theOperations System (OS) (per Bellcore's recommendations in GR-253(GR-253: Synchronous Optical Network (SONET) Transport Systems, CommonGeneric Criteria, Issue 2 [Bellcore, December 1995], included herein byreference, in its entirety and for all purposes)). Preferably, whenusing SONET, the handling of the LOS condition follows Bellcore'srecommendations in GR-253, which allows nodes to inter-operate, andco-exist, with other network equipment (NE) in the same network. A pathrestoration protocol is invoked as soon as the LOS defect is detected bythe line card, which occurs 3 ms following the failure (a requirementunder GR-253).

Under GR-253, downstream is in the direction of the failure, andupstream is opposite in direction to the failure. A defect in thedirection from the source to the destination would therefore cause anAIS to be propagated upstream and an RDI to be propagated downstream.The arrival of the AIS at the node upstream from the failure causes theupstream node to send a similar alarm to its upstream neighbor and forthat node to send an AIS to its own upstream neighbor. This continuesfrom node to node until the AIS finally reaches the source node of theaffected VP, or a proxy node if the source node is located in adifferent zone. Under GR-253, each node is allowed a maximum of 125microseconds to forward the AIS upstream, which quickly propagatesfailures toward the source (or proxy) node.

Once a node detects a failure on one of its links, either through alocal LOS defect or a received AIS indication, the node scans its VPtable looking for entries for VPs that include the failed link andanalyzes the mode of failure.

Failure Modes:

There can be many virtual path-related failure modes in a networkdepending upon the location of link failure in that network. Virtualpath failure modes can be characterized as follows:

Neighbor or Link mode: In this mode, the failure occurs at any physicalport of a link between two adjacent nodes. The scope of the notificationand restoration messages is preferably limited to the two adjacent nodesthat discover the failure. Restoration, in this case, is relatively fastbecause the restoration does not involve the resource of any other nodein the network (including proxy or source node). The inter-nodalphysical path traversed by the VP also does not change.

Path mode: In this mode, path failures are much more broader than aphysical port breakdown. This may include a failure of entire opticallink or a node. The source and destination of the affected VPs arenotified and potentially the entire network is involved in therestoration. This mode may involve more messaging and longer restorationtime than the Link mode. However, it depends on the CoS of the VP thathow fast the path will be restored. Restoration here will most likelychange the path traversed by the VP.

Failure Restoration:

FIG. 2 is a flow diagram of broad general steps performed by a node forrestoration in response to the failure of a virtual path. As noted, thefailure of a link, results in a LOS condition at the nodes connected tothe link and generates the appropriate AIS and RDI indications. If anAIS or RDI was received from a node, a failure has been detected (step200). In that case, each affected node performs several actions in orderto maintain accurate status information with regard to the VPs currentlysupported. The first action taken in such a case is that the node scansits VP table (step 210) looking for entries that have the failed link intheir path (step 220). If the VP does not use the failed link, the nodegoes to the next VP in the table and begins analyzing that entry (step230). If the selected VP uses the failed link, the node determines ifthe failure is a physical port failure (step 240). If the failure is aphysical port failure then the node performs local link mode restoration(step 260). If the failure is not a physical port failure then the nodeinitiates a path mode restoration for failed VP (step 250).

Neighbor or Link mode restoration: FIG. 3A is a flow diagram of stepsperformed in response to the failure of a port on a link between twoadjacent neighbor nodes. Link mode notification and restoration isachieved by means of exchanging a Restore Span packet. The Link modefailure messages may be likened to SONET APS except for the fact thatthe contents of link mode messages are much richer and thus gives moreflexibility and resilience to multiple failures during the restorationprocedure.

Once a node detects a failure on one of its active ports (step 300),either through a local loss of signal defect or a received errorindication, the node scans the VP table (step 302) and checks to see ifthe port is in use by a VP (step 304). Further action depends upon thetype of VP i.e. the associated CoS. If the port is not assigned to anyVP, no action is taken and the node proceeds to next VP in the table(step 306). If the failed port is used by a VP, which requiresrestoration then the node that detected the failure, determines if thefailure is physical port failure (step 308). If the failure is notlocal, the node initiates path restoration by initiating a Restore_Irequest (step 310).

If the failure is a physical port failure, the node first determines ifextra ports are available within the same link (step 312). If extraports are not available then the node initiates path restoration request(step 310). Once an extra physical port is identified, the nodeinitiates a Restore Span request (step 314), switches the port (step316) and logs event in node database (step 318).

FIG. 3B illustrates an example of a Restore Span packet. The RestoreSpan packet (320) is used to restore a VP from port or fiber failureslocally. Restore Span packet contains the Identification of VP beingrestored (325) and the total bandwidth required to restore VP (330). TheIndex of failed port on Master node (335) identifies the port thatfailed and the Index of failed port on Slave node (340) identifies theport on slave side. A Fill field (345) is provided for slave node toprovide an index of suggested port to replace the failed port on Masternode.

The Restore Span requests are preferably generated by the master nodeand replied to by the slave node on the link. This allows traffic fromone or more ports to be switched to other unused ports on the same link.One advantage of using this procedure is that the process only involvestwo nodes and preserves the resources of other nodes in the network(including source and destination). After receiving a Restore Spanpacket, the slave node responses with a Restore Span response packet.

FIG. 3C illustrates an example of a Restore Span Response packet whichis identical to Restore Span request packet. In the Restore SpanResponse packet (350), the slave node provides an index (355) ofsuggested port to replace failed port of VP. This operation does notinvolve any other nodes or the network. The path is restored without theinterruption of service on the virtual path.

If the failure is more serious than just a simple port failure i.e. anentire link is down (and no port is active) then the failure affects allthe traffic on failed link. In this case, the network goes into pathmode restoration.

Path mode restoration: If local Link mode restoration fails or entirelink is down then the node which discovers the failure creates and sendsout a Restore_I packet. Restore_I packets are path messages in that theyare sent down the same path as the VP that traversed the failed link.

FIG. 3D illustrates an example of a Restore_I packet. The Restore_Ipacket (360) contains the Identification of failed VP (365), PhysicalInstance Identification of the VP (370) that the node originating theRestore_I packet has and the attempt count of the current physicalinstance of the Virtual Path (375). The Restore_I packet also containsthe direction of the failure (380). The direction field indicateswhether the failure occurred on the UPSTREAM (towards the Source of theVP) or DOWNSTREAM (towards Destination) side of the node. The failedpath field (385) indicates whether the path is the Primary or Secondarypath for CoS-3. For all other types of VPs, this field indicates thatfailed path is the primary path for failed VP.

Initiating Restore_I Request: The node that discovers the failuretransmits Restore_I packets both upstream and downstream. The source ofthe VP only transmits them downstream. After transmitting packet, thesource node immediately starts restoration process. The destination nodesends packets upstream and after sending these packets, the node startsa timer for acknowledgement and retransmission.

The intermediate or tandem node attempt to send packets in bothdirections, even in the case that there is no transmission path in oneof the directions. Restore_I packet transmissions are reliable andpreferably are acknowledged by the receiving node (the neighbor of theinitiating node). A timer is started for each Restore_I request that issent. The request is resent periodically until a response is received ora threshold for the number of unacknowledged packets sent is reached. Ineither case, if an acknowledgment is received or the threshold isreached, then all resources associated with the VP are released. In thecase of multiple port failure in the same VP, even if Restore_I messagesare sent out regarding the failure of the first port in a VP, uponsubsequent failures, similar procedure is carried out. FIG. 3Cillustrates a format of the Restore_I message.

Receiving Restore_I Request:

Upon receiving a Restore_I packet, certain tests are performed. A nodeshould examine the VP ID and return a NAK (with a reason code ofNULL_VP) if this VP doesn't exist at the node. For VP with a lower CoS,the state of the VP and Path is changed to DOWN. When source node of alower CoS VP receives a Restore_I packet, then the source node willgenerate an alarm. For VPs with a CoS requiring Dynamic MeshRestoration, if the receiving node is a tandem node, then the currentPhysical Instance (PI) of the VP at the node is compared to the PI inthe Restore_I packet. If the stored PI at the node is higher than theone in the Restore_I packet, then a NAK (STALE_MSG) is returned (to thesending node). Otherwise, the Restore_I packet is accepted forprocessing. The state of the VP is changed to DOWN, if the state is notalready set in that state. The Restore_I packet is then forwarded in thesame direction as the incoming packet. A timer is initiated forretransmission and after certain predefined threshold timesretransmissions, all the resources of VP are released.

If the receiving node is the Source node of the VP, the source nodestarts restoration and the state of path is set to RESTORING. If thereceiving node is the destination node then all the resources associatedwith the VP are released and the node waits for messages from the Sourceto arrive. In all the cases (except when a NAK has to be returned), anACK is returned to the node sending the packet.

Receiving a Restore_I Response:

If the receiving node has already responded to Restore_I packet thenresponses to subsequent Restore_I packets are ignored if the PhysicalInstance of the VP in the response is lower than the node's currentPhysical Instance for that VP. For valid responses, the appropriatetimer and retransmissions are stopped. If receiving node is tandem nodeand the response is positive and responses to all the packets sent outfor that VP have been received, then the resources allocated to the VPare released.

For negative responses, the reason code is examined and if the number ofretries is below a given threshold, the sending node resends theRestore_I packet. If this threshold has been exceeded, resourcesassociated with the VP are released. Similarly, if the reason code isSTALE_MSG (possibly because the responding node has already participatedin the set up of a new restoration path for the VP and thus has a higherPhysical Instance now), resources for the VP are released without anyretransmissions.

Initiating Path Restoration:

Processing by Source/Proxy Node:

When the node receiving Restore_I packet is the source or proxy node ofthe VP then the node acknowledges the request packet and the VP isplaced on a list of VPs to be restored. The state of VP is set toRESTORING and the node starts restoration process.

FIG. 4A is a flow diagram of general steps performed by a source orproxy node in response to the failure of a link. As noted, the failureof a link results in a LOS condition at the nodes connected to thefailed link and generates appropriate AIS and RDI indications. When anAIS or RDI message is received from a node, the message indicatesdetection of a failure (step 400). In that case, each affected nodeperforms several actions in order to maintain accurate statusinformation with regard to the VPs currently supported. The first actiontaken in such a case is that the node scans its VP table, looking forentries that have the failed link in their path (steps 405). Next, thenode checks if the VP uses the failed link (step 410). If the VP doesnot use the failed link, the node goes to the next VP in the table (step415). If the selected VP uses the failed link, the node changes VP'sstate to RESTORING (step 420) and releases all link bandwidth allocatedto that VP (step 425). The node places VP on the list of VPs to berestored (step 430).

Next, the source or proxy node sends a Restore Path Request packet (RPR)to all eligible neighbors (i.e., a node adjacent to the given node) inorder to restore the given VP. Neighbor eligibility is determined by thestate of the neighbor, available link bandwidth, current zone topology,location of the target node, and other parameters.

The Restore Path Packet:

FIG. 4B illustrates an example of a Restore Path Request (RPR) packet.The Restore Path packet is sent by the source nodes (or proxy boundarynodes), to obtain an end-to-end path for a VP. The packet is usuallysent during failure recovery procedures but can also be used forprovisioning new VPs. The RPR packet (440) includes a virtual pathidentifier field (445) and a reserved flag field (450). The requestedbandwidth for failed virtual path is indicated in bandwidth field (455).The Path Length field (460) indicates the number of links in the VP.This field determines how many Link IDs appear at the end of the packet.A HOP_COUNT field (465) is provided to determine the number of nodes theRestore Path Request packed has traveled. This field is set to 0 by thesource node and is incremented at every node during the floodingprocedure. An array of path lengths (470) is provided to identify thelinks used by each intermediary node to replace the failed VP. Each nodethat processes Restore Path Request will populate this field with thelink used for VP restoration. MAX_HOP field (475) defines the maximumnumber of nodes to be included in the path.

The Processing of Received RPRs by Tandem Node

Due to the way RPR messages are forwarded by tandem nodes and theunconditional and periodic retransmission of such messages by originnodes, multiple instances of the same request and even multiple copiesof each instance, circulating in the network at any given time is notuncommon. To minimize the amount of broadcast traffic generated by theprotocol and aid tandem nodes in allocating bandwidth fairly forcompeting RPRs, tandem nodes preferably executes a sequence such as thatdescribed subsequently.

The term “same instance,” as used herein, refers to messages that carrythe same VP ID, origin node ID and hop-count, and are received from thesame tandem node (usually, the same input link, assuming only one linkbetween nodes). Any two messages that meet the above criteria areguaranteed to have been sent by the same origin node, over the samelink, to restore the same VP, and to have traversed the same path. Theterms “copy of an instance,” or more simply “copy” are used herein torefer to a retransmission of a given instance. Normally, tandem nodesselect the first instance they receive because in most, but not allcases, as the first RPR received normally represents the quickest pathto the origin node. To keep track of all the requests, the nodemaintains RPR related information in a Restore Path Request Entry datastructure.

The Restore-Path Request Entry (RPRE) is a data structure that maintainsinformation about a specific instance of a RPR packet. Tandem nodes usethe structure to store information about the request, which helps themidentify and reject other instances of the request, and allows them tocorrelate received responses with forwarded requests. Table 1 lists anexample of the fields that are preferably present in an RPRE. Other pathrelevant information can also be added to the structure.

TABLE 1 RPR Fields Field Usage Origin Node The node ID of the node thatoriginated this request. This is either the source node of the VP or aproxy node. Target Node Node ID of the target node of the restore pathrequest. This is either the destination node of the VP or a proxy node.Received From The neighbor from which we received this message. FirstSequence Number Sequence number of the first received copy of thecorresponding restore-path request. Last Sequence Number Sequence numberof the last received copy of the corresponding restore-path request.Bandwidth Requested bandwidth. QoS Requested QoS. Timer Used by the nodeto timeout the RPR. T-Bit Set to 1 when a Terminate indicator isreceived from any of the neighbors. Pending Replies Number of theneighbors that haven't acknowledged this message yet. Sent To A list ofall neighbors that received a copy of this message. Each entry containsthe following information about the neighbor: AckReceived: Indicates ifa response has been received from this neighbor. F-Bit: Set to 1 whenFlush indicator from this neighbor.

When an RPR packet arrives at a tandem node, a decision is made as towhich neighbor should receive a copy of the packet. The choice ofneighbors is related to variables such as link capacity and distance.Specifically, a particular neighbor is selected to receive a copy of thepacket if:

-   -   1. The output link has enough resources to satisfy the requested        bandwidth.    -   2. The path through the neighbor is less than MAX_HOPS in        length. In other words, the distance from this node to the        target node is less than MAX_HOPS minus the distance from this        node to the origin node.    -   3. The node hasn't returned a Flush response for this specific        instance of the RPR, or a Terminate response for this or any        other instance.

FIG. 5 illustrates the actions performed by tandem nodes in processingreceived RPR tests. Assuming that this is the first instance of therequest, the node allocates the requested bandwidth on eligible linksand transmits a modified copy of the received message onto them. Thebandwidth remains allocated until a response (either positive ornegative) is received from the neighboring node, or a positive responseis received from any of the other neighbors (see Table 8 below). Whileawaiting a response from its neighbors, the node cannot use theallocated bandwidth to restore other VPs, regardless of their priority.

Processing of RPRs begins at step 500, in which the target node's ID iscompared to the local node's ID. If the local node's ID is equal to thetarget node's ID, the local node is the target of the RPR and mustprocess the RPR as such. This is illustrated in FIG. 5 as step 505 andis the subject of the flow diagram illustrated in FIG. 6. If the localnode is not the target node, the RPR's HOP_COUNT is compared to MAX_HOPin order to determine if the HOP_COUNT has exceeded or will exceed themaximum number of hops allowable (step 510). If this is the case, anegative acknowledgment (NAK) with a Flush indicator is then sent backto the originating node (step 515). If the HOP_COUNT is still withinacceptable limits, the node then determines whether this is the firstinstance of the RPR having been received (step 520). If this is thecase, a Restore-Path Request Entry (RPRE) is created for the request(step 525). This is done by creating the RPRE and setting the RPRE'sfields, including starting a time-to-live (TTL) or deletion timer, inthe following manner:

-   -   RPRE.SourceNode=Header.Origin    -   RPRE.Destination Node=Header.Target    -   RPRE.FirstSequence Number=Header.SequenceNumber    -   RPRE.Last Sequence Number=Header.Sequence Number    -   RPRE.QoS=Header.Parms.RestorePath.QoS    -   RPRE.Bandwidth=Header. Parms.RestorePath.Bandwidth    -   RPRE.ReceivedFrom=Node ID of the neighbor that sent us this        message StartTimer (RPRE.Timer, RPR_TTL)

The ID of the input link is then added to the path in the RPRE (e.g.,Path[PathIndex++]=LinkID) (step 530). Next, the local node determineswhether the target node is a direct neighbor (step 535). If the targetnode is not a direct neighbor of the local node, a copy of the(modified) RPR is sent to all eligible neighbors (step 540). ThePendingReplies and SentTo Fields of the corresponding RPRE are alsoupdated. If the target node is a direct neighbor of the local node, theRPR is sent only to the target node (step 545). In either case, the RPREcorresponding to the given RPR is then updated (step 550).

If this is not the first instance of the RPR received by the node, thenode then attempts to determine whether this might be a differentinstance of the RPR (step 555). A request is considered to be adifferent instance if the RPR:

-   -   1. Carries the same origin node IDs in its header;    -   2. Specifies the same VP ID; and    -   3. Was either received from a different neighbor or has a        different HOP_COUNT in its header.

If this is simply a different instance of the RPR, and another instanceof the same RPR has been processed, and accepted, by this node, a NAKWrong Instance is sent to the originating neighbor (step 560). Theresponse follows the reverse of the path carried in the packet. Nobroadcasting is therefore necessary in such a case. If a similarinstance of the RPR has been processed and accepted by this node (step565), the node then determines whether a Terminate NAK has been receivedfor this RPR (step 570). If a Terminate NAK has been received for thisRPR, the RPR is rejected by sending a Terminate response to theoriginating neighbor (step 575). If a Terminate NAK was not received forthis RPR, the new sequence number is recorded (step 580) and a copy ofthe RPR is forwarded to all eligible neighbors that have not sent aFlush response to the local node for the same instance of this RPR (step585). This may include nodes that weren't previously considered by thisnode due to conflicts with other VPs, but does not include nodes fromwhich a Flush response has already been received for the same instanceof this RPR. The node then saves the number of sent requests in thePendingReplies field of the corresponding RPRE. The term “eligibleneighbors” refers to all adjacent nodes that are connected through linksthat meet the link-eligibility requirements previously described.Preferably, bandwidth is allocated only once for each request so thatsubsequent transmissions of the request do not consume any bandwidth.

Note that the bandwidth allocated for a given RPR is releaseddifferently depending on the type of response received by the node andthe setting of the Flush and Terminate indicators in its header. Table 2shows the action taken by a tandem node upon receiving a restore pathresponse from a neighbor.

TABLE 2 Actions taken by a tandem node upon receiving an RPR. ReceivedResponse Flush Terminate Sequence Type Indicator? Indicator? NumberAction X X X Not Valid Ignore response Negative No No 1 = Last Ignoreresponse Negative X No =Last Release bandwidth allocated for the VP onthe link on which the response was received. Negative Yes No ValidRelease bandwidth allocated for the VP on the link on which the responsewas received. Negative X Yes Valid Release all bandwidth allocated forthe VP. Positive X X Valid Commit bandwidth allocated for the VP on thelink the response was received on; release all other bandwidth.The Processing of Received RPRs by Destination or Target Node

FIG. 6 illustrates the process performed at the target node once the RPRfinally reaches that node. When the RPR reaches its designated targetnode, the target node begins processing of the RPR by first determiningwhether this is the first instance of this RPR that has been received(step 600). If that is not the case, a NAK is sent with a Terminateindicator sent to the originating node (step 605). If this is the firstinstance of the RPR received, the target node determines whether or notthe VP specified in the RPR actually terminates at this node (step 610).If the VP does not terminate at this node, the target node again sends aNAK with a Terminate to the originating node (step 605). By sending aNAK with a Terminate indicator, resources allocated along the path arefreed by the corresponding tandem nodes.

If the VP specified in the RPR terminates at this node (i.e. this nodeis indeed the target node), the target node determines whether an RPREexists for the RPR received (step 615). If an RPRE already exists forthis RPR, the existing RPRE is updated (e.g., the RPRE'sLastSequenceNumber field is updated) (step 620) and the RPRE deletiontimer is restarted (step 625). If no RPRE exists for this RPR in thetarget node (i.e., if this is the first copy of the instance received),an RPRE is created (step 630). Pertinent information from the RPR iscopied into the RPRE (step 635), the bandwidth requested in the RPR isallocated on the input link by the target node (step 640) and an RPREdeletion timer is started (step 645). In either case, once the RPRE iseither updated or created, a checksum is computed for the RPR (step 650)and written into the checksum field of the RPR (step 655). The RPR isthen returned as a positive response to the origin node (step 660). Thelocal (target) node then initiates its own matrix configuration. It willbe noted that the RPRE created is not strictly necessary but helps toensure that the processing of RPRs is consistent across nodes.

The Processing of Received RPR Responses by the Origination Node:

FIGS. 7 and 8 are flow diagrams illustrating the processes performed byoriginating nodes that receive negative and positive RPR responses,respectively. Negative RPR responses are processed as depicted in FIG.7. An originating node begins processing a negative RPR response bydetermining whether the node has an RPRE associated with the RPR (step700). If the receiving node does not have an RPRE for the received RPRresponse, the RPR response is ignored (step 705). If an associated RPREis found, the receiving node determines whether the node sending the RPRresponse is listed in the RPRE (e.g., is actually in the SentTo list ofthe RPRE) (step 710). If the sending node is not listed in the RPRE,again the RPR response is ignored (step 705).

If the sending node is listed in the RPRE, the RPR sequence number isanalyzed to determine its validity (step 715). As with the previoussteps, if the RPR contains an invalid sequence number (e.g., doesn'tfall between FirstSequenceNumber and LastSequence Number, inclusive),the RPR response is ignored (step 705). If the RPR sequence number isvalid, the receiving node determines whether Flush or Terminate in theRPR response (step 720). If neither of these is specified, the RPRresponse sequence number is compared to that stored in the last sequencefield of the RPR (step 725). If the RPR response sequence number doesnot match that found in the last sequence field of the RPRE, the RPRresponse is again ignored (step 705). If the RPR response sequencenumber matches that found in the RPRE, or a Flush or Terminate wasspecified in the RPR, the input link on which the RPR response wasreceived is compared to that listed in the RPR response path field(e.g., Response.Path[Response.PathIndex]==InputLinkID) (step 730). Ifthe input link is consistent with information in the RPR, the next hopinformation in the RPR is checked for consistency (e.g.,Response.Path[Response.PathIndex+1]==RPRE.ReceivedFrom) (step 735). Ifeither of the proceeding two tests are failed, the RPR response is againignored (step 705).

If a Terminate was specified in the RPR response (step 740), thebandwidth on all links over which the RPR was forwarded is freed (step745) and the Terminate and Flush bits from the RPR response are saved inthe RPRE (step 750). If a Terminate was not specified in the RPRresponse, bandwidth is freed only on the input link (i.e., the link fromwhich the response was received) (step 755). The Terminate and Flushbits are saved in the RPRE (step 760), and the Flush bit of the RPR iscleared (step 765). If a Terminate was not specified in the RPR, thePending Replies field in the RPRE is decremented (step 770). If thisfield remains non-zero after being decremented, the process completes.If Pending Replies is equal to zero at this point, or a Terminate wasnot specified in the RPR, the RPR is sent to the node specified in theRPR's Received From field (i.e. the node that sent the correspondingrequest) (step 780). Next, the bandwidth allocated on the link to thenode specified in the RPR's Received From field is released (step 785),and an RPR deletion timer is started (step 790).

FIG. 8 illustrates the steps taken in processing positive RPR responses.The processing of positive RPR responses begins at step 800 with asearch of the local database to determine whether an RPRE correspondingto the RPR response is stored therein. If a corresponding RPRE cannot befound, the RPR response is ignored (step 810). If the RPR response RPREis found in the local database, the input link is verified as beingconsistent with the path stored in the RPR (step 820). If the input linkis not consistent with the RPR path, the RPR response is ignored onceagain (step 810). If the input link is consistent with path informationin the RPR, the next hop information specified in the RPR response pathis compared with the Received From field of the RPRE (e.g.,Response.Path[Response.PathIndex+1]!=RPRE.ReceivedFrom) (step 830). Ifthe next hop information is not consistent, the RPR response is againignored (step 810). However, if the RPR response's next hop informationis consistent, bandwidth allocated on input and output links related tothe RPR is committed (step 840). Conversely, bandwidth allocated on allother input and output links for that VP is freed at this time (step850). Additionally, a positive response is sent to the node from whichthe RPR was received (step 860), and an RPR deletion timer is started(step 870) and the local matrix is configured (step 880).

With regard to matrix configuration, the protocol pipelines suchactivity with the forwarding of RPRs in order to minimize the impact ofmatrix configuration overhead on the time required for restoration.While the response is making its way from node N1 to node N2, node N1 isbusy configuring its matrix. In most cases, by the time the responsereaches the origin node, all nodes along the path have alreadyconfigured their matrices.

The Terminate indicator prevents “bad” instances of an RPR fromcirculating around the network for extended periods of time. Theindicator is propagated all the way back to the originating node andprevents the originating node, and all other nodes along the path, fromsending or forwarding other copies of the corresponding RPR instance.

Terminating RPR Packets are processed as follows. The RPR continuesalong the path until one or more of the following four conditions areencountered:

-   -   1. Its HOP_COUNT reaches the maximum allowed (i.e. MAX_HOPS).    -   2. The request reaches a node that doesn't have enough bandwidth        on any of its output links to satisfy the request.    -   3. The request reaches a node that had previously accepted a        different instance of the same request from another neighbor.    -   4. The request reaches its ultimate destination: the target        node, which is either the Destination node of the VP, or a proxy        node if the Source and Destination nodes are located in        difference zones.        Conditions 1, 2 and 3 cause a negative response (NAK) to be sent        back to the originating node, flowing along the path carried in        the request, but in the reverse direction.

Further optimizations of the protocol can easily be envisioned by one ofskill in the art and are intended to be within the scope of thisspecification. For example, in one embodiment, a mechanism is defined tofurther reduce the amount of broadcast traffic generated for any givenVP. In order to prevent an upstream neighbor from sending the sameinstance of an RPR every T milliseconds, a tandem node can immediatelyreturn a no-commit positive response to that neighbor, which preventsthe neighbor from sending further copies of the instance. The responsesimply acknowledges the receipt of the request, and doesn't commit thesender to any of the requested resources. Preferably, however, thesender (of the positive response) periodically transmits theacknowledged request until a valid response is received from itsdownstream neighbor(s). This mechanism implements a piece-wise, orhop-by-hop, acknowledgment strategy that limits the scope ofretransmitted packets to a region that gets progressively smaller as thepacket gets closer to its target node.

Optimizations

However, it is prudent to provide some optimizations for the efficienthandling of errors. Communication protocols often handle link errors bystarting a timer after every transmission and, if a valid response isn'treceived within the timeout period, the message is retransmitted. If aresponse isn't received after a certain number of retransmission, thesender generates a local error and disables the connection. The timeoutperiod is usually a configurable parameter, but in some cases thetimeout period is computed dynamically, and continuously, by the two endpoints. The simplest form of this uses some multiple of the averageround trip time as a timeout period, while others use complexmathematical formulas to determine this value. Depending on the distancebetween the two nodes, the speed of link that connects them, and thelatency of the equipment along the path, the timeout period can rangeanywhere from millisecond to seconds.

The above strategy of handling link errors can be improved upon,however, the fast restoration times required dictate that 2-way,end-to-end communication be carried out in less than 50 ms. A limitationof the above-described solution is the time wasted while waiting for anacknowledgment to come back from the receiving node. A safe timeoutperiod for a 2000 mile span, for instance, can be 35 ms or more, inwhich case there is not enough time for a retransmission in case of anerror.

This problem is addressed in one embodiment by taking advantage of themultiple communication channels (i.e. OC-48's) that exist between nodesto:

-   -   1. Send N copies (N>=1) of the same request over as many        channels, and    -   2. Re-send the request every T milliseconds (1 ms<10 ms) until a        valid response is received from the destination node.

Preferably, the amount of packets sent is carefully controlled that thebroadcast does not create congestion in the network. The link efficiencyis improved further by using small packets during the restorationprocedure. The present invention can be practiced on a networknode/element such as that described below.

FIG. 9 is a block diagram illustrating network environment in which acommercial transaction processing system according to the presentinvention may be practiced. As is illustrated in FIG. 9, a network 900,such as a private wide area network (WAN) or the Internet includes anumber of networked servers 910(1)-(N) that are accessible by clientterminals 912(1)-(N). Communication between client terminals 912(1)-(N)and servers 910(1)-(N) typically occurs over a publicly accessiblenetwork, such as a public switched telephone network over ADSL telephonelines or large bandwidth trunks, for example communications channelsproviding T1 or OC3 service. Client terminals 912(1)-(N) access servers910(1)-(N) through a service provider, e.g., an Internet serviceprovider such as America On-Line™, Prodigy™, CompuServe™ and the like,by executing application specific software, commonly referred to as abrowser, on one of client terminals 912(1)-(N).

One or more of client terminals 912(1)-(N) and/or one or more of servers910(1)-(N) may be, for example, a computer system of any appropriatedesign, in general, including a mainframe, a mini-computer or a personalcomputer system. Such a computer system typically includes a system unithaving a system processor and associated volatile and non-volatilememory, one or more display monitors and keyboards, one or more diskettedrives, one or more fixed disk storage devices and one or more printers.These computer systems are typically information handling systems, whichare designed to provide computing power to one or more users, eitherlocally or remotely. Such a computer system may also include one or aplurality of I/O devices (i.e. peripheral devices) which are coupled tothe system processor and which perform specialized functions. Examplesof I/O devices include modems, sound and video devices and specializedcommunication devices. Mass storage devices such as hard disks, CD-ROMdrives and magneto-optical drives may also be provided either as anintegrated or peripheral device. One such exemplary computer systemdiscussed in terms of client terminals 912(1)-(N) is shown in detail inFIG. 10.

FIG. 10 depicts a block diagram of a host computer system 1000 suitablefor implementing the present invention, and exemplary of one or more ofclient terminals 912(1)-(N). Host computer system 1000 includes a bus1012 which interconnects major subsystems of host computer system 1000.These subsystems include a central processor 1014, a system memory 1016(typically RAM, but which may also include ROM, flash RAM, or the like),an input/output controller 1018, an external audio device such as aspeaker system 1020 via an audio output interface 1022, an externaldevice such as a display screen 1024 via display adapter 1026, serialports 1028 and 1030, a keyboard 1032 (interfaced with a keyboardcontroller 1033), a storage interface 1034, a floppy disk drive 1036operative to receive a floppy disk 1038, and a CD-ROM drive 1040operative to receive a CD-ROM 1042. Also included are a mouse 1046 (orother point-and-click device, coupled to bus 1012 via serial port 1028),a modem 1047 (coupled to bus 1012 via serial port 1030) and a networkinterface 1048 (coupled directly to bus 1012).

Bus 1012 allows data communication between central processor 1014 andsystem memory 1016, which may include both read only memory (ROM) orflash memory (neither shown), and random access memory (RAM) (notshown), as previously noted. The RAM is generally the main memory intowhich the operating system and application programs are loaded andtypically affords at least 16 megabytes of memory space. The ROM orflash memory may contain, among other code, the Basic Input-Outputsystem (BIOS) which controls basic hardware operation such as theinteraction with peripheral components. Applications resident with hostcomputer system 1000 are generally stored on and accessed via a computerreadable medium, such as a hard disk drive (e.g., fixed disk 1044), anoptical drive (e.g., CD-ROM drive 1040), floppy disk unit 1036 or otherstorage medium. Additionally, applications may be in the form ofelectronic signals modulated in accordance with the application and datacommunication technology when accessed via network modem 1047 orinterface 1048.

Storage interface 1034, as with the other storage interfaces of hostcomputer system 1000, may connect to a standard computer readable mediumfor storage and/or retrieval of information, such as a fixed disk drive1044. Fixed disk drive 1044 may be a part of host computer system 1000or may be separate and accessed through other interface systems. Manyother devices can be connected such as a mouse 1046 connected to bus1012 via serial port 1028, a modem 1047 connected to bus 1012 via serialport 1030 and a network interface 1048 connected directly to bus 1012.Modem 1047 may provide a direct connection to a remote server via atelephone link or to the Internet via an internet service provider(ISP). Network interface 1048 may provide a direct connection to aremote server via a direct network link to the Internet via a POP (pointof presence).

Many other devices or subsystems (not shown) may be connected in asimilar manner. Conversely, it is not necessary for all of the devicesshown in FIG. 10 to be present to practice the present invention. Thedevices and subsystems may be interconnected in different ways from thatshown in FIG. 10. The operation of a computer system such as that shownin FIG. 10 is readily known in the art and is not discussed in detail inthis application. Code to implement the present invention may beoperably disposed or stored in computer-readable storage media such asone or more of system memory 1016, fixed disk 1044, CD-ROM 1042, orfloppy disk 1038.

It will be noted that the variable identifier “N” is used in severalinstances in FIG. 10 to more simply designate the final element (e.g.,servers 910(1)-(N) and client terminals 912(1)-(N)) of a series ofrelated or similar elements (e.g., servers and client terminals). Therepeated use of such variable identifiers is not meant to imply acorrelation between the sizes of such series of elements, although suchcorrelation may exist. The use of such variable identifiers does notrequire that each series of elements have the same number of elements asanother series delimited by the same variable identifier. Rather, ineach instance of use, the variable identified by “N” may hold the sameor a different value than other instances of the same variableidentifier.

Moreover, regarding the signals described herein, those skilled in theart will recognize that a signal may be directly transmitted from afirst block to a second block, or a signal may be modified (e.g.,amplified, attenuated, delayed, latched, buffered, inverted, filtered orotherwise modified) between the blocks. Although the signals of theabove described embodiment are characterized as transmitted from oneblock to the next, other embodiments of the present invention mayinclude modified signals in place of such directly transmitted signalsas long as the informational and/or functional aspect of the signal istransmitted between blocks. To some extent, a signal input at a secondblock may be conceptualized as a second signal derived from a firstsignal output from a first block due to physical limitations of thecircuitry involved (e.g., there will inevitably be some attenuation anddelay). Therefore, as used herein, a second signal derived from a firstsignal includes the first signal or any modifications to the firstsignal, whether due to circuit limitations or due to passage throughother circuit elements which do not change the informational and/orfinal functional aspect of the first signal.

The foregoing described embodiment wherein the different components arecontained within different other components (e.g., the various elementsshown as components of host computer system 1000). It is to beunderstood that such depicted architectures are merely exemplary, andthat in fact many other architectures can be implemented which achievethe same functionality. In an abstract, but still definite sense, anyarrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality.

FIG. 11 depicts the interconnection of host computer system 1000 toclient systems 1110, 1120 and 1130. FIG. 11 depicts internetwork 11100(e.g., the Internet) interconnecting client systems 1110, 1120 and 1130.With reference to host computer system 1000, modem 1047 or some othernetwork interface can be used to provide connectivity from host computersystem 1000 to internetwork 1100. Protocols for exchanging data via theInternet are well known to those skilled in the art. Although FIG. 11depicts the use of the Internet for exchanging data, the presentinvention is not limited to the Internet or any particular network-basedenvironment.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein, changes and modifications may be madewithout departing from this invention and its broader aspects and,therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims.

1. A method comprising: restoring a virtual path over a physical path inan optical network, wherein the restoring comprises: detecting a failurewithin a link between a first node and a second node of the physicalpath, analyzing the failure within the link to determine whether a linkrestoration procedure is adequate to restore the virtual path,performing the link restoration procedure if the analyzing indicatesthat the link restoration procedure is adequate to restore the virtualpath, wherein the link restoration procedure comprises: transmitting aport identification query, and receiving, in response to the portidentification query, an indication of a replacement port for restoringthe virtual path, and performing a path restoration procedure if theanalyzing indicates that the link restoration procedure is not adequateto restore the virtual path, wherein the path restoration procedurecomprises determining an alternate physical path after the failure. 2.The method of claim 1, wherein the link comprises a plurality of ports,the failure within the link is a port failure of a first port within thelink, and the ports comprise the first port.
 3. The method of claim 2,wherein the analyzing comprises: determining if at least one other ofthe ports is available to replace the first port within the link,wherein the at least one other of the ports is a one of the ports otherthan the first port.
 4. The method of claim 3, further comprising: if atleast one other of the ports is available to replace the first portwithin the link, performing the link restoration procedure.
 5. Themethod of claim 4, wherein the link restoration procedure comprises:restoring the virtual path to a second port of the at least one other ofthe ports.
 6. The method of claim 4, wherein the link restorationprocedure comprises: restoring the virtual path to a second port of theat least one other of the ports using the first node.
 7. The method ofclaim 3, further comprising: if none of the ports other than the firstport is available to replace the first port within the link, performingthe path restoration procedure.
 8. The method of claim 7, wherein thepath restoration procedure comprises: restoring the virtual path to thealternate physical path.
 9. The method of claim 3, further comprising:if at least one other of the ports is available within the link,performing the link restoration procedure; and otherwise, performing thepath restoration procedure.
 10. The method of claim 9, wherein the pathrestoration procedure comprises: restoring the virtual path to thealternate physical path.
 11. The method of claim 1, wherein the pathrestoration procedure comprises: broadcasting a plurality of resourcerequest packets to a plurality of nodes in the optical network;dynamically identifying a plurality of nodes with resources wherein thenodes with resources are ones of the nodes having a resource necessaryto support the virtual path; wherein the alternate physical pathcomprises ones of the nodes with resources; configuring the alternatephysical path by establishing a communication connection between theones of the nodes with resources; and provisioning the virtual path overthe alternate physical path.
 12. The method of claim 11, furthercomprising: if at least one other of the ports is available to replacethe first port within the link, performing the link restorationprocedure.
 13. The method of claim 11, further comprising: if at leastone other of the ports is available within the link, performing the linkrestoration procedure; and otherwise, performing the path restorationprocedure.
 14. The method of claim 11, wherein: the broadcasting theplurality of resource request packets comprises transmitting a requestmessage from a first node of a network to a second node of the opticalnetwork, the dynamically identifying the plurality of nodes withresources comprises temporarily allocating a resource on at least one ofthe first and second nodes, the establishing the communicationconnection between the ones of the nodes with resources comprisesreceiving a response message at the first node, in response to therequest message, and the configuring the alternate physical pathcomprises configuring the temporarily allocated resource as a dedicatedresource for the alternate physical path.
 15. The method of claim 1,wherein the transmitting the port identification query comprises thefirst node transmitting the port identification query to the second nodeon the link; and the receiving the indication comprises the first nodereceiving the indication from the second node.
 16. The method of claim1, wherein the path restoration procedure comprises acts performed by atleast one node in the optical network other than the first and secondnodes.
 17. The method of claim 1, wherein the link restoration procedureconsists of acts performed within the first and second node and actsperformed between the first and second node.
 18. A computer-readablemedium having a plurality of instructions executable by a processor,wherein the plurality of instructions, when executed, cause theprocessor to perform a method for restoring a virtual path over aphysical path in an optical network, the method comprising: detecting afailure within a link between a first node and a second node of thephysical path, analyzing the failure within the link to determinewhether a link restoration procedure is adequate to restore the virtualpath, performing the link restoration procedure if the analyzingindicates that the link restoration procedure is adequate to restore thevirtual path, wherein the link restoration procedure comprises:transmitting a port identification query, and receiving, in response tothe port identification cluery, an indication of a replacement port forrestoring the virtual path, and performing a path restoration procedureif the analyzing indicates that the link restoration procedure is notadequate to restore the virtual path, wherein the path restorationprocedure comprises determining an alternate physical path after thefailure.
 19. The computer-readable medium of claim 18, wherein the linkcomprises a plurality of ports, the failure within the link is a portfailure of a first port within the link, and the ports comprise thefirst port; wherein the analyzing comprises determining if at least oneother of the ports is available to replace the first port within thelink, wherein the at least one other of the ports is a one of the portsother than the first port.
 20. The computer-readable medium of claim 14,further comprising: if at least one other of the ports is available toreplace the first port within the link, performing the link restorationprocedure.
 21. The computer-readable medium of claim 14, furthercomprising: if none of the ports other than the first port is availableto replace the first port within the link, performing the pathrestoration procedure.
 22. The computer-readable medium of claim 14,further comprising: if at least one other of the ports is availablewithin the link, performing the link restoration procedure; andotherwise, performing the path restoration procedure, wherein the pathrestoration procedure comprises restoring the virtual path to thealternate physical path.
 23. The computer-readable medium of claim 18,wherein the path restoration procedure comprises: broadcasting aplurality of resource request packets to a plurality of nodes in theoptical network; dynamically identifying a plurality of nodes withresources wherein the nodes with resources are ones of the nodes havinga resource necessary to support the virtual path; configuring thealternate physical path by establishing a communication connectionbetween the ones of the nodes with resources; and provisioning thevirtual path over the alternate physical path.
 24. The computer-readablemedium of claim 23, further comprising: if at least one other of theports is available within the link, performing the link restorationprocedure; and otherwise, performing the path restoration procedure. 25.The computer-readable medium of claim 23, wherein: the broadcasting theplurality of resource request packets comprises transmitting a requestmessage from a first node of a network to a second node of the opticalnetwork, the dynamically identifying the plurality of nodes withresources comprises temporarily allocating a resource on at least one ofthe first and second nodes, the establishing the communicationconnection between the ones of the nodes with resources comprisesreceiving a response message at the first node, in response to therequest message, and the configuring the alternate physical pathcomprises configuring the temporarily allocated resource as a dedicatedresource for the alternate physical path.
 26. The computer-readablemedium of claim 18, wherein the transmitting the port identificationquery comprises the first node transmitting the port identificationquery to the second node on the link; and the receiving the indicationcomprises the first node receiving the indication from the second node.27. The computer-readable medium of claim 18, wherein the pathrestoration procedure comprises acts performed by at least one node inthe optical network other than the first and second nodes.
 28. Thecomputer-readable medium of claim 18, wherein the link restorationprocedure consists of acts performed within the first and second nodeand acts performed between the first and second node.
 29. A system forrestoring a virtual path over a physical path in an optical network, thesystem comprising: means for detecting a failure within a link between afirst node and a second node of the physical path; means for analyzingthe failure within the link and deciding whether a link restorationprocedure is adequate to restore the virtual path; means for performingthe link restoration procedure if the analyzing indicates that the linkrestoration procedure is adequate to restore the virtual path, whereinthe means for performing the link restoration procedure comprises: meansfor transmitting a port identification query, and means for receiving,in response to the port identification query, an indication of areplacement port for restoring the virtual path, and means forperforming a path restoration procedure if the analyzing indicates thatthe link restoration procedure is not adequate to restore the virtualpath, wherein the path restoration procedure comprises determining analternate physical path after the failure.
 30. The system of claim 24,wherein the means for transmitting the port identification querycomprises means for transmitting the port identification query from thefirst node to the second node on the link; and the means for receivingcomprises means for receiving the indication of the replacement port forrestoring the virtual path from the second node.
 31. The system of claim24, wherein the path restoration procedure comprises acts performed byat least one node in the optical network other than the first and secondnodes.
 32. The system of claim 29, wherein the link restorationprocedure consists of acts performed within the first and second nodeand acts performed between the first and second node.